1. Field of the Invention
The present invention relates to a dismantling method and a recycling method for a magnetic field generator, and more specifically to a dismantling method and a recycling method for a magnetic field generator comprising neodymium magnets and used in a large MRI apparatus capable of scanning a human body.
2. Description of the Related Art
Size of the neodymium magnet, which is a sintered body, is limited. Usually therefore, in this kind of large magnetic field generator, a plurality of neodymium magnets are fixed to a plate yoke by an adhesive.
A method for dismantling such a magnetic field generator can be as follows: Specifically, screws connecting the plate yokes to column yokes are loosened, then the magnetic field generator is suspended by a crane, and disassembled. Each of the plate yokes is then bathed in a drum filled with solvent for melting the adhesive, and the neodymium magnets fixed to the plate yokes are taken out.
However, the neodymium magnets, as magnetized, have a very strong magnetism. Therefore, according to the above-mentioned method, it is dangerous because the neodymium magnets will be thrown out of the drum by strong repelling force among the neodymium magnets once the adhesive loses its adhering strength. Another potential danger is that a worker's hand can be caught between two neodymium magnets for example, by strong magnetic attraction, when one of the neodymium magnets is pulled off from another.
Further, the neodymium magnet is a sintered body which is fragile. Thus, once the adhesive loses its adhering strength, if the magnet is thrown by a magnetic repelling force acting among the neodymium magnets and hits something, the magnet will be chipped.
Further, if the neodymium magnet hits another neodymium magnet or the plate yoke, a spark will be generated, which may cause fire or explosion accident.
There may be an idea that the neodymium magnets are demagnetized by applying demagnetizing magnetic field at the time of dismantling the magnetic field generator. However, the magnetic field generator for MRI apparatus is large, and therefore demagnetizing operation, in which a strong and large magnetic field must be generated, is difficult. A large demagnetizing equipment is not realistic due to a high cost.
The Japanese Patent Publication (of examined Application for opposition) No. 3-20045 discloses a method, in which each of permanent magnets is first magnetized, then measured for its magnetic characteristic, then heated to demagnetize, and at a time of assembly, each of the magnets is re-magnetized in accordance with its magnetic characteristic for assembly into a magnet body. However, this method is for appropriately disposing the permanent magnets, and nothing has been disclosed for a method for dismantling or recycling the large magnetic field generator.